Gas blast electric circuit breaker



Feb..l0, 1942. w. K. RANKIN GAS ELAST ELECTRIC CIRCUIT BREAKER v FiledOct. 29, 1940 2 Sheets-Sheet 1 6 WV/////// v I 2 c l m 7/// ////////A/E// ///fl/// w L '6 6 9 "6 F 4 E h 1 u m 2 Q my & m om. M m 5 w 2 m Q na n l 2 a m 0 O0 w M a a o o 0. E 3 M o l Ea m m w 7 Q m I I m Inventor.I William Kfiankin,

IS Attorney F 10. 1942- w. K. RANKIN I 2 212 224 GAS BLAST ELECTRICCIRCUIT BREAKER Filed Oct. 29, 1940 2 Sheets-Sheet 2 ATMOSPHERIC AIRInventor: William K. Rankin,

Has Attorn ey.

Patented Feb. 10, 1942 2,272,224 GAS BLAST ELECTRIC CIRCUIT BREAKERWilliam K. Rankin, Lansdowne, la., assignor to General Electric Comp NewYork any, a corporation of Application October 29, 1940, Serial No.363,325

12 Claims.

My invention relates to electric circuit breakers of the gas blast type,particularly to air blast circuit breakers employing an insulating arcchute in which the arc is extinguished by a blast of air under pressure,and has for its principal object the provision of improved arc chutestructure for preventing 'or minimizing to a practical extent theemission of flame from the arc chute during interruption of largecurrent arcs.

The interruption of heavy current power arcs by a gas blast is oftenaccompanied by a great deal of flame composed of incandescent particlesof are products including metal or other inorganicsubstances, andburning gases. This flameis obviously very objectionable if notcompletely confined, particularly in indoor stations since it tends tobreak downthe dielectric strength of the surrounding air and therebycause failure of the circuit breaker and also possible damage toadjacent apparatus. Furthermore, flame emission from the circuit breakercasing cannot be tolerated where there isa possibility of injury tostation attendants.

It has been proposed to employ gas mufflers and various cooling devicesat the exhaust part of the arc chamber for cooling the gases andsuppressing or minimizing the emission of flame but arrangementsheretofore used have in general been either inadequate in the case oflarge current interruptions or have required excessive space.

In accordance with my invention, flame emission from the circuit breakeris substantially precluded by so directing the gas blast including thehot gases flowing from the region of arcing through a chamber ofsufllcient size that rapid burning of combustible and incandescent gasesis facilitated within said chamber in the presence of an excess ofoxygen. In a preferred embodiment of my invention, this isaccomplished'by directing the air blast through the are near its initialpoint of formation to extinguish the arc, and subsequently mixing in acombustion chamber connected to or forming a part of the arc chute theresulting hot blast and a supply of fresh air. Since there is. notalways sufficient oxygen in the interrupting blast to satisfy therequirements for complete combustion of all combustible gases andproducts involved, the introduction of fresh air in the arc chute servesto promote combustion of unburned gas, etc; so that it does not igniteupon reaching the atmosphere. For the purpose of this specification, theterm are chute is defined to comprehend the complete arc chamber andflame preventing structure.

My invention will be more fully set forth in the following descriptionreferring to the accompanying drawings, and the features of noveltywhich characterize my invention will be pointed out with particularityinthe claims annexed to and forming a part of this specification.

Referring to the drawings, Fig. 1 is a sectional view of a gas blastcircuit breaker embodying the present invention, Fig. 2 is a sectionalview taken along the line 22 of Fig. 1, Fig. 3 is an elevational view,partly broken away, of another form of gas blast circuit breaker myinvention may assume, Fig. 4 is a similar view of a modified form of myinvention and Figs. 5, 6' and 7 are enlarged views of the structure ofFig. 4.

The circuit breaker illustrated by way of example in Fig. l is of theair blast type and comprises the conductor terminals l and 2 to whichthe flxed contacts 3 and 4 are connected respectively. The contact 4which is in slidin contact with terminal 2 comprises a reciprocallymovable blade member arranged to engage the finger contacts 3 of thestationary contact. The movable contact is suitably controlled andoperated by mechanismnot shown and the fixed contact is mounted in aninsulating casing 5 defining the arc chamber and constituting a part ofthe arc chute.

As illustrated by Fig. 2, the casing 5 comprises insulating sidewalls 6coating with insulating end walls 1 to form a narrow fan-shaped arcchute leading from the coacting contacts. The contacts themselvesseparate within a narrow slotlike passage defined by the insulatingmembers 6' composed preferably of hard fibre and this passage is incommunication with an air supply conduit 8 which is arranged to beconnected to a suitable source of air pressure, such as a reservoir orcompressor unit. The control means for admitting air under pressure tothe arc chute upon separation of the contacts form no part of thepresent invention and are omitted in the interest of simplicity.

' Suitablearc extinguishing means, such as hard fibre barriers 9, extendfan-wise from the arc path between the insulating sidewalls 6 so as todivide the arc chute into a plurality of diverging passages, Anadditional insulating fibre barrier Ill extends continuously throughoutthe arc chamber with the exception of a slot ID of sumcient sizetoreceive the blade contact 4. The extinguishing structure including thebarriers {l and I0 is composed of a'suitable organic vaporizablematerial and in addition to hard fibre may consist of materials such asurea or methylmethacrylate. These materials, although vaporizable underthe influence of heavy arcs do not become conducting as in the case ofceramic materials.

In the arrangement so far described, admission of an air blast to theentrance of the arc chamber at H in accordance with separation of thecontacts is effective to drive the are which forms between the extendedstationary finger contacts 3 and the arcing tip 4 of the movable contactinto the arc chute passages so as to impinge directly on the exposededges of the fibre barriers 9. As the hot blast flowing from the regionof the arc is directed into the diverging chute passages, it soonencounters cooling structure defined by spaced copper plates I2extending across the path of gas flow as illustrated by Fig. 2. Thiscooling structure, while effectively reducing the temperature andreducing the volume of the highly heated blast gases so as to minimizeback pressure, may not, however, prevent flame emission beyond thebarriers 9. in the case of heavy current interruptions.

The air blast circuit breaker so far described in connection with Figs.1 and 2 is disclosed and claimed in an application Serial No. 303,126,filed November 6, 1939, by D. C. Prince et al. for Circult breakingapparatus and method of operating the same, and assigned to the sameassignee as the present invention. Although Fig. 1 and Fig. 2 of thepresent application are shown in the aforesaid Prince et al.application, no

claims involving the gas exhaust conduit connected to the arc chute aremade in that application, such claims being made in the presentapplication, the invention of which is animprovement on the invention ofsaid Prince et al. application.

It is known that insulating arc extinguishing structure composed oforganic material such as hard fibre vaporizes when subjected to theintense heat of arcing. I have found that the resulting gases whichinclude hydrogen, hydrocarbon gases and carbon monoxide are responsibleto a great extent for the flame above described, particularly when thesegases are vented to atmosphere in a highly heated state. The oxygen inthe atmosphere at once unites with the highly heated combustible gasesto cause burning thereof so that considerable flame may exist exteriorlyof the breaker itself. I have also found that an oxygen containingblast, such as air blast, can be utilized in combination with circuitbreaker structure so as to cause substantially complete I combustion ofthese gases to atmosphere.

For the purpose of causing more complete burning of combustible gasesand eliminating flame emission from the breaker, an insulating conduitI3 is connected to the casing 5 so as to be in direct communication withthe exhaust ends of the diverging chute passages. That end of theconduit nearest the point of initial formation of the arc, i. e. the endreceiving the blast from the first diverging passage i4, is closed by aninsulating wall I5. The opposite end of the conduit indicated at I6exhausts to atmosprior to their venting ,phere. The conduit i3, whichcan conveniently comprise a cylindrical tube of insulation is suitablyattached to the chute walls asindicated at 6" and is cut away at l3 toreceive the blast gases from the arc chamber. It is somewhat longer thanindicated by Fig. 1 for the purpose of providing more combustion spaceand al lowing more complete combustion of the gases before they arefinally vented to atmosphere.

In practice, this type of air blast circuit breakor is generallyeffective to interrupt arcing alter the movable contact has uncoveredbut one or two of the chute passages. Accordingly, the hot blast ismainly directed through the first passage M and the adjacent passage ll.The following passages 18 and 19 generally receive a comparatively freshand cool air blast after are interruption so that there may be an excessof oxy gen, insofar as combustion requirements are concerned, within theconduit. In the case of long arcs, the passage 20 can be relied upon,after clearing of the slot in, for supplying fresh air to the conduitI3.

It will therefore be observed that since the arc may be consideredinterrupted generally by the time the movable contact reaches the secondbarrier 9, the most highly heated arc gases contaming vaporized fibredriven by the air blast into the chute are confined to the first one ortwo chute passages. Therefore, the last passage at least, i. e. thepassage defined by the barrier or partition ill and the adjacentpartition ii, is

' available to direct comparatively fresh and cool blast air into thechute. Since the hot arc gases directed into the exhaust conduit 13 nearits closed end must mix with this comparatively cool fresh air beforeleaving the conduit combustion chamber, it will be apparent that theexhaust gases are not only appreciably cooled before flnal venting butare also burned in the presence of an excess of oxygen in the combustionspace deflned by the conduit i3. Flame emission from the conduit in thecase of heavy duty operation is thereby either eliminated or greatlyminimized. Although involving asomewhat more complicated arrangement, itwill be apparent that an oxygen-containing gas or fresh air supplyindependent of the main blast supply conduit 8 may, if desired, beintroduced by way of the passage 20 at any time prior to or during theinterrupting operation.

In another form of my invention, the combustion space is increased forthe purpose of handling exceptionallyv large amounts of flame incidentto heavy overload and short circuit interruptions. In addition, thehighly heated arc gases are so diverted as to insure complete mixingwith the comparatively cool and fresh air blast which is also directedinto the combustion chamber. A circuit breaker employing this principleis shown by Fig. 3, certain speciflc features and constructional detailsof which are claimed in an application Serial No. 310,603, filedDecember 22, 1939 by L. J. Linde for Air blast circuit breaker.

Referring now to Fig. 3, the circuit breaker comprises a fixed contactstru cture.3ll including a plurality of spring pressed fingers, and acoacting movable contact 31 which is operated by any suitable mechanism(not shown) generally in the manner of Fig. 1 through an oscillatableinsulating arm 32 connected thereto by a. crosshead 33. The fixedcontact 38 is connected to are are driven during the interruptingoperation of the breaker. The are confining hamber 31, as illustrated byFigs. 1 and 2, ispreferably shaped to fit rather closel over theopposite sides of the movable contact so that th passages formed by thebarriers 39 are substantially shut off from the gas blast from conduit38 when the.

contacts are closed and are progressively opened during separatingmovement of the contacts.

With this construction, the passages formed by the barriers 39 open atone end at longitudinally spaced points along the path of contactseparation, i. e. the region of arcing, and each is adapted to receivethe gases from the corresponding section of the arc path. Each of thepassages formed by the barriers and the lateral walls of the arcconfining chamber is provided with a plurality of spacedcooling plates40 of good heatconducting material, such as copper.

Since, as previously stated, in this type breaker the arc is usuallyinterrupted at an earl point in the separating movement of therelatively movable contacts, the hottest gases emerging from the arcchamber come from the passages .of the arc chute opening adjacent to thfixed contact 30. As previously pointed out, these gases often contain aconsiderable percentage of unburned combustible gas. This lattercondition exists, particularly, in circuit breakers where the barriers39 and the arc confining chamber 31 are formed of organic material, suchas urea resin or hard fibre, which has a tendency to evaporate under theaction of the arc.

In this arrangement, the gases from the arc chamber are confined untilthey are completely burned and sufficiently cooled before they areexhausted to the atmosphere. The construction is also designed toutilize to best advantage the available space in an air blast breakerunit which is of such a size and shape that it may be interchanged withoil breaker units of th same rating as are now in service. Asillustrated in the drawing, the gases from the arc confining chamber 31pass through the passages formed by the barriers 39 and through anopening in the side of an elongated insulating housing 4| which extendsin a direction generally perpendicular to the barriers 39. The housing4|, which is generally rectangular in cross-section, is closed at oneend and at the other end opens into an exhaust tube 42. In theconstruction illustrated by way of example, the tube extends upwardly sothat the hot gases are exhausted in that direction. The interior of thehousing is divided int upper passages 43 and 44 and a lower passage 45by a longitudinally extending partition member 48 and an extendedbarrier 39 ofthe ar chute. The partition member 45 terminates aconsiderable distance from eachend of the housing so that the passages43 and 45 are in communication adjacent to the closed end of the housingand the passages 44 and 45 merge near the'open end of the housing 4| toform an enlarged free space 41 in which the gases from passages 44 andmay mix and burn. In the drawings the arc confining chamber 31 and thehousing 4| are illustrated as integrally formed. It is to be understood,however, that the entire insulating structure may be fabricated fromsuitable sheet insulating material.

In order to provide for rapid cooling of the gases within the housing 4|a pluralit of stacks of cooling plates 48, 49 and 50 are provided in thepassages 43, 44 and 45 respectively. The metal plates are suitablyspaced so as to permit free passage of gas through the passages.

The advantages of the above described construction'will be betterunderstood after a description of the circuit interrupting operation ofthe breaker. As the relatively movable contacts are separated an arc isdrawn therebetween. In timed relation with the separation of thecontacts a blast of air, or other ar extinguishing gas, is supplied tothe arc chamber through the conduit 38. The blast may be controlled byany suitable means (not shown) such as a blast valve operated by thecontact operating mechanism. The arc is blown against the edge of thefibre barriers 39 and into the diverging passages formed thereby Whereit is extinguished and the circuit interrupted. In this interruptingprocess the arc is first elongated as it bends over the edges of thebarriers 39 until it finally divides into serially related sectionswhich are separated by the barriers. After interruption of the are,however, the gases, and particularly those from the vicinity of thefixed contact 30, are highly heated and incandescent and generallycontain a considerable percentage of unburned gases.

As previously pointed out, this is particularly true where the barriers39 are formed of hard fibre or other organic insulating material havingthe property of evaporating sufiiciently under the action of the arc toprevent the ends of the barriers from becoming conductive during thecircuit interrupting operation.

In the present design, the gases from the vicinity of the fixed contact30 are directed toward the closed end of the housing 4| and thenreturned to the open end of the housing through two stacks of coolingplates 48 and 50. other hand, the gases from the opposite side of thearcing chamber are directed into the chamber 41- at the open end of thehousing 4| by way of the short passage 44. At this point, the twocurrents of gas are mixed in a combustion chamber of suitable sizebefore they are vented through the tube 42 in a cooled and harmlessstate.

The gases from the upper passage 44 contain a very small percentage ofcombustible gas and in the case of air blast comprise mostly fresh airso that an excess of oxygen exists in the chamber 41. This mixture ofthe gases from the upper and lower passages within-the chamber 41 beforethey are exhausted to atmosphere provides for the complete combustion ofany unburned gases from the lower passage 45. Thus it is seen that thehottest gases and those containing combustible gases in quantity are ledthrough a circuitous path to a combustion space, while the comparativelycool and less combustible gases from that portion of the path of contacttravel remote from the fixed contact are led directly to the combustionspace where the gases may mix and burn. This division of gases from thearc chamber makes it possible to exhaust to atmosphere gases which arenot detrimental to the surrounding equipment or dangerous to person- Onthe nel. In addition the amount of space for so handling the gases isnot excessive.

It has been found with this construction that under the severestoperating conditions no flame or excessively hot gases are emittedi'romthe upper end of the exhaust tube 42. The construction also takesadvantage of all the available space in a circuit breaker unit of thesize and shape required for substitution in the metal clad units whichhave previously found widespread application in oil circuit breakerinstallations.

In the form of my invention shown by Figs. 4 to 7 inclusive, the hotblast gases directed into the combustion chamber are mixed with freshair that is drawn into the chamber directly from the atmosphere. Inother words, the fresh air supply for insuring combustion of carbonmonoxide, et cetera, is independent of the blast source although theblast action is utilized for the purpose of introducing it into thecombustion chamber. Specifically, this can be accomplished by directingthe gas blast past openings in the chute structure connecting withatmosphere so that by inductive action fresh air is drawn directly intothe chute or combustion chamber for mixing with the hot blast gases.With this arrangement, the fresh air supply can be admitted well beyondthe point of arcing so that a supply of cool, oxygen-containing gas isalways provided regardless of the possibility of unusually prolongedarcing.

Referring more particularly to the drawings, Fig. 4 shows an arc chuteconstruction generally similar to Fig. l and the same reference numeralsare used to indicate similar parts. In the case of the cooling platesl2, however, an altogether different arrangement is employed involvingsocalled inductor grids 60. These grids each comprise, in a convenientconstruction, a sheet of good heat conducting metal, such as copper,folded in V form as more clearly shown by Fig. 5 so that the apex of theV faces the gas blast. The grids 3|] are located in the blast passagesbetween the insulating partitions 9 generally in the manner of Fig. 1except that the leading edges extend transversely of, instead ofparallel to, the arc path. The grids are spaced to form passages Gl fordirecting the blast gases into the combustion space defined by theexhaust tube 13.

For the purpose of introducing a fresh air supply .directly fromatmosphere to the chute by means of the inductive action of the blast,the insulating side walls of the chute structure 5 are provided withopenings directly connecting the space within the fold of each V shapedgrid to atmosphere. This is bestillustrated by Figs. 6 and 7, Figf6being a sectional view taken along the line 6-6 of Fig. 5. Asshown byFig. s the insulating side walls of the chute structure 5 are cut awayat 62 at both side edges of the grids '60. The blast spaces 6| betweenthe grids are closed at the openings 62 by strips 83 of suitablematerial as best shown by Fig. 7 so that the gas blast itself cannotprematurely escape to atmosphere but must flow directly into thecombustion space at 13. I However, the space 64 defined within the foldof each grid 60 is directly connected to atmosphere at both sides of thechute so that the gas blast, by its inductive action as it flows pasteach grid 50, draws in fresh air from both sides of the chute asindicated by the flow direction arrows of Fig. 7. In other words, thegrid arrangement functions somewhat as aspirating apparatus for thepurpose of drawing fresh air into the chute.

It will therefore be seen that an independent supply of oxygenmontaininggas is introduced by and in accordance with the operation of the gasblast into the combustion chamber well beyond the point of arcing. Byreason of the number of fresh air openings, it will also be seen thatthe fresh air supply is thoroughly and uniformly mixed with the hotblast gases practically immediately upon entry to the combustion space.It should furthermore be noted that fresh air supply may be provided asabove described either in combination with the arrangements previouslydisclosed or so as to constitute substantially the soleoxygen-containing gas supply.

The spaced grid member construction which I have described and shown inFigs. 4 to 7 for introducing fresh air from atmosphere into thecombustion space and which is involved in one of the claims of thepresent application is an improvement on the invention disclosed in thecopending application of D. Prince, for "Gas blast circuit breaker,Serial No. 395,579, filed May'Zi}, 1941, and assigned to the sameassignee as the present application. The Prince application containsclaims covering this construction generically while I have limited myclaim so as not to read on the disclosure of said Prince applicationsince Prince is the prior inventor of such generic invention.

It should be understood that my invention is not limited to specificdetails of construction and arrangement thereof herein illustrated, andthat changes and modifications may occur to one skilled in the artwithout departing from the spirit of my invention.

"What I claim as new and desire to secure by Letters Patent of theUnited States is:

1. A gas blast circuit breaker comprising relatively movable contacts,means for directing a gas blast through the arc gap formed uponseparation of said contacts, insulating arc extinguishing structureincluding organic vaporizable material into which said gas blast isdirected for extinguishing said arc, said structure also defining acombustion space, and means for guiding hot combustible blast gasesflowing from the region of said are so as to mix with a supply ofcomparatively cool gas after arc interruption within said combustionspace prior to venting of the exhaust gases to atmosphere.

2. An air blast circuit breaker comprising relatively movable contacts,means for directing an air blast through the arc gap formed uponseparation of said contacts, organic insulating material definingarcjextinguishing structure into which said air blast is directed'forextinguishing said are, a combustion space in communication with saidare extinguishing structure, and means for guiding the highly heatedblast gases including combustible gases flowing from said areextinguishing structure so as to mix with a supply of comparativelyfresh air within said combustion chamber prior to venting of the exhaustgases to atmosphere.

3. An air blast circuit breaker comprising relatively movable contacts,means for directing an air blast through the arc gap formed uponseparation of said contacts, arc extinguishing structure composed ofvaporizable material disposed closely adjacent and in confining relationto said are gap so as to be subject to vaporization under influence ofthe are heat, and means defining a combustion space into which the blastgases from said are gap are directed, and means for guiding said blastgases so that the highly heated gas and vaporized material flowing fromthe are proper is caused to mix with a comparatively fresh air blastwithin said combustion space prior to final venting of said gases andvaporized fibre to atmosphere.

4. A gas blast circuit breaker comprising relatively movable contacts,means for directing a gas blast through the arc gap formed uponseparation of said contacts, an insulating arc chute structureforreceiving said gas blast as it tra-' verses said are gap andfor-confining the arc dur- V,

the initially opened passage with comparatively fresh gases fromsubsequently opened passages within said chamber.

5. A gas blast circuit breaker comprising relatively movable contacts,means for directing a gas blast transversely through the arc gap formedupon separation of said contacts and an insulating arc chute structureinto which the arc is driven by said gas blast, said are chute includingbarriers forming passages adjacent said are gap arranged to be opened tosaid blast in succession in accordance with separation of saidcontacts,.a combustion chamber in communication with said passages, saidchamber having an exhaust vent, and deflecting means in said structurefor causing flow of the most highly heated blast gases traversing theinitially opened passage through a longer path to said exhaust vent thanthe gases through subsequently opened passages so that said heated blastgases are caused to mix with the gases from said subsequently openedpassages.

6. A gas blast circuit breaker for heavy duty power circuit interruptioncomprising relatively movable contacts, means for directing a blast ofgas transversely across the arc gap formed upon separation of saidcontacts, an insulating arc chute into which the arc is driven by saidblast, said chute at the side of said'arc gap opposite the entrance ofsaid gas blast having a plurality of insulating partitions disposededgewise to said are dividing the chute into separate passage leadingfrom" serially related parts of said are gap to the chute exhaust, and agas exhaust chamber defining a combustion space into which all saidpassages lead, said chamber extending in a direction generallytransversely of said partitions so as to cause mixing of the blast gasesfrom all said passages within said combustion space.

'7. An air blast circuit breaker for heavy duty power circuitinterruption comprising relatively movable contacts, means for directinga blast of air transversely across the arc gap formed upon separation ofsaid contacts, an insulating arc chute into which the arc is driven bysaid blast, said chute at the side of said are gap opposite the entranceof said air blast having a plurality of insulating partitions disposededgewise to said are dividing the chute into separate diverging passagesleading from points longitudinally spaced along said are gap to thechute exhaust,

said air blast being effective to interrupt arcing well within saidchute'prior to extension of the arc gap to all said passages, and aconduit defining a gas exhaust and combustion chamber into which allsaid passages lead, said conduit extending in a direction generallytransversely of said partitions to exhaust at the end corresponding tothe last formed part of the arc gap whereby hot arc gases entering saidconduit from the initially formed part of the are are caused to mix withcomparatively cool fresh air directed into said chamber from the chutepassage nearest the exhaust end of said conduit.

8. A gas blast circuit breaker comprising relatively movable contacts,means for supplying a gas blast to the arc gap formed upon separation ofsaid contacts, an insulating arc chute structure including organicvaporizable material for directing said gas blast through said are gapfor interruption of the are adjacent to said material, said structurealso defining a combustion space into which the blast gases aredirected, and means for directing comparatively fresh air into saidcombustion space to mix with highly heated combustible arc gases formedincident to the interruption of the are within said are chute structureprior to venting of the exhaust gases from said combustion space. 9. Agas blast circuit breaker comprising relatively movable contacts, meansfor directing a gas blast through the arc gap formed upon separation ofsaid contacts, insulating arc chute structure in which said arc isinterrupted by said gas blast, said chute structure defining acombustion space into which the highly heated blast gases from the areare directed, and means for causing by and in accordance with theoperation of said gas blast, introduction of comparatively fresh airinto said combustion space to mix with said highly heated gases prior tothe venting of gases from said combustion space.

10. A gas blast circuit breaker comprising relatively movable contacts,means for directing a gas blast through the arc gap formed uponseparation of said contacts, insulating arc chute structure in whichsaid are is interrupted by said gas blast, said chute structure defininga combustion space into which the highly heated blast gases from the areare directed, and a plurality of spaced grid members in said chutestructure disposed in the path of said gas blast, said members formingpassages connecting with atmosphere and leading in the direction of saidblast into said combustion space arranged so as to cause by aspirationintroduction of fresh air from atmosphere into said combustion space tomix with said highly heated blast gases prior to venting of said heatedgases from said combustion space.

11. A gas blast circuit breaker for power circuit interruptioncomprising relatively fixed and movable contacts, means for directing ablast of gas through the arc gap formed upon separation of saidcontacts, an insulating arc chute into which the arc is driven by saidblast, said chute at the side of said are gap opposite the entrance ofsaid gas blast having a plurality of partitions disposed edgewise tosaid arc dividing the chute into separate passages leading from seriallyrelated parts of said arc gap to the chute exhaust, said gas blast beingeffective to interrupt arcing within said chute prior to extension ofthe arc gap to all said passages, and a gas exhaust chamber into whichall said passages lead, said chamber extending laterally of saidpassages in a direction generally transversely of said partitions 10gases to atmosphere.

of said are gap to the chute exhaust, portions 0! said are chuteadjacent to said are gap being composed of an organic vaporizablematerial, said. air blast being effective to interrupt arcing within.said chute prior to extension of the arc gap to all said passages, and agas exhaust chamber into which all said passages lead so as to causemixing of hot combustible blast gases and comparatively cool blast airprior to venting of the exhaust WILLIAM K. RANKIN.

